1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system and a method of manufacturing such a magnetic head, and to a head assembly and a hard disk drive each of which includes the magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
For magnetic read/write devices such as magnetic disk drives, higher recording density has been constantly required to achieve a higher storage capacity and smaller dimensions. Typically, magnetic heads used in magnetic read/write devices are those having a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
Write heads include those of a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and those of a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. Recently, the shift from the longitudinal magnetic recording system to the perpendicular magnetic recording system has been promoted in order to achieve higher recording density of magnetic read/write devices.
The write head for the perpendicular magnetic recording system incorporates a coil for generating a magnetic field corresponding to data to be written on a recording medium, and a pole layer for allowing a magnetic flux corresponding to the magnetic field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium. The pole layer has an end face located in a medium facing surface, and the width of the end face defines the track width.
As magnetic heads for perpendicular magnetic recording, a magnetic head incorporating first and second shields disposed to sandwich a pole layer in between is known, as disclosed in U.S. Pat. No. 7,126,788 B1, for example. In this magnetic head, at the medium facing surface, the end face of the first shield is located backward of the end face of the pole layer along the direction of travel of the recording medium with a specific distance provided therebetween. The end face of the second shield is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific distance provided therebetween. The first and second shields have a function of preventing a magnetic flux from reaching the recording medium, the flux having been generated from the end face of the pole layer and expanding in directions except the direction orthogonal to the surface of the recording medium. The magnetic head incorporating such first and second shields makes it possible to achieve a further improvement in recording density.
In the magnetic head incorporating the first and second shields, a first gap layer is disposed between the first shield and the pole layer, and a second gap layer is disposed between the second shield and the pole layer. Each of the first and second gap layers is made of a nonmagnetic material.
Here is given a description of a method of forming the pole layer in a case in which the first shield is located closer to the substrate than the second shield. In this case, the first gap layer is formed on the first shield, the pole layer is formed on the first gap layer, the second gap layer is formed on the pole layer, and the second shield is formed on the second gap layer. The pole layer is formed by frame plating, for example. In this case, a photoresist layer is first formed on the first gap layer, and the photoresist layer is patterned by photolithography to form a frame. The frame has a groove having a shape corresponding to the shape of the pole layer to be formed. Next, a plating layer that will be the pole layer is formed in the groove of the frame by plating.
The following problem arises in the case in which the pole layer is formed on the first gap layer by frame plating as described above. When the photoresist layer is patterned by photolithography, light used for exposing the photoresist layer passes through the photoresist layer, and then further passes through the first gap layer and gets reflected off the top surface of the first shield, and returns to the photoresist layer. As a result, a standing wave is generated in the photoresist layer. Consequently, the wall surface of the frame forming the groove will be formed into an irregular surface, not a flat surface. Since the plating layer grows with a shape that reflects the shape of the wall surface of the frame forming the groove, if the wall surface has irregularities, there may occur a case in which the groove is not completely filled with the plating layer and small cavities are formed in the plating layer. In this case, the resulting pole layer will include small cavities, that is, defects. Furthermore, if the wall surface of the frame forming the groove has irregularities, great variations occur in width of the pole layer, which results in variations in track width.